1. Field of the Invention
The present invention relates to a drum brake preferable for an industrial vehicle such as a fork lift truck. Specifically, the present invention relates to an improvement in achieving a light-weighted structure for reducing production cost and achieving promotion of maintenance performance.
2. Description of the Related Art
FIG. 5 and FIG. 6 show a conventional example of a drum brake for braking a front wheel of a fork lift truck.
The drum brake 1 is disclosed in JP-A-11-201203 and is constituted by providing a drum 5 formed in a headed cylindrical shape and integrally rotated with a front wheel tire 3; a pair of brake shoes 7 and 8 arranged to be opposed to each other at the inside of the drum 5; a shoe drive mechanism 9 for expanding the brake shoes 7 and 8 toward an inner peripheral face of the drum 5; an anchor pin 11 applied with brake torque by being brought into contact with end portions of the brake shoes 7 and 8; a backing plate 13 having a circular disc portion 13a on which side edges 7a and 8a of the respective brake shoes 7 and 8 slidingly move and a cover portion 13b extended from an outer periphery of the circular disc portion 13a in an axial direction for covering an outer peripheral portion of the drum 5; and a mount bracket 15 having a portion thereof attached with the backing plate 13 and fixed to a vehicle body.
As shown in FIG. 5, the mount bracket 15 is integrally formed with a first flange portion 15a fastened to a frame 17 on the vehicle side by a screw 19; a second flange portion 15c formed with a shaft inserting hole 15b inserted with a drive shaft 21 of the front wheel tire 3 at its center; and a sleeve 15d formed in a cylindrical shape concentric with the shaft inserting hole 15b. The mount bracket 15 is formed by casting or the like.
The illustrated shoe drive mechanism 9 is a wheel cylinder 9a arranged between opposed ends of the pair of brake shoes 7 and 8 on one side and operated by hydraulic pressure. The pair of brake shoes are expanded by urging the end portions of the pair of brake shoes in directions separating from each other.
The wheel cylinder 9a is fixed to the circular disc portion 13a of the backing plate 13.
The pair of brake shoes 7 and 8 are supported by the circular disc portion 13a of the backing plate 13 operable to expand by shoe hold-down pins, not illustrated.
As shown in FIG. 6, the backing plate 13, attached with the pair of brake shoes 7 and 8 and the shoe drive mechanism 9, is fixed to the second flange portion 15c of the mount bracket 15 via a stud bolt 23.
The cover portion 13b of the backing plate 13 functions as a dust cover for preventing foreign matter from invading from the outside into the drum 5.
The anchor pin 11 is fixedly fastened by a screw member 25 in a state of being inserted to both of the circular disc portion 13a of the backing plate 13 and the second flange portion 15c of the mount bracket 15.
In the case of the above-described conventional drum brake 1, the backing plate 13 is formed by pressing. On the other hand, since the mount bracket 15 is constructed by a three-dimensional structure in which the sleeve 15d is projected relative to the first flange portion 15a and the second flange portion 15c, casting or forging is needed as a method of producing the mount bracket 15. Therefore, there poses a problem that production cost is increased highly since there are needed not only a pressing facility but also a facility for precision casting or the like in a production line. Furthermore, according to the mount bracket 15 produced in this way, its weight is increased.
Moreover, the circular disc portion 13a of the backing plate 13, on which the side edges 7a and 8a of the brake shoes 7 and 8 slidingly move in braking, is worn by repeating braking operation and needs to be replaced. However, according to the above-described conventional drum brake 1, the backing plate 13 is attached with the brake shoes 7 and 8, the shoe drive mechanism 9 and the anchor pin 11; therefore, when the backing plate 13 is replaced due to wear thereof, an article to be replaced is obliged to reassemble again after temporarily removing all of attached parts. This poses a problem that maintenance performance is poor in replacing the backing plate or the like.
The present invention has been carried out in view of the above-described situation and it is an object thereof to provide a drum brake capable of forming a mount bracket by pressing and capable of reducing production cost by omitting a facility for precision casting or the like in a production line. At the same time, it is an object of the present invention to provide a drum brake capable of achieving a light-weighted structure of a product, further, excellent in maintenance performance by dispensing with removal or reattachment of a brake shoe, a shoe drive mechanism and the like when a backing plate is replaced in accordance with wear of a sliding portion thereof.
In order to achieve the above-described object, according to the invention, there is provided a drum brake comprising: a pair of brake shoes arranged opposedly to each other in a drum; a shoe drive mechanism for expanding the brake shoes toward an inner peripheral face of the drum; an anchor pin applied with a brake torque by being brought into contact with end portions of the brake shoes in braking; a backing plate having a circular disc portion on which side edges of the respective brake shoes slidingly move and a cover portion extended from an outer periphery of the circular disc portion in an axial direction for covering an outer peripheral portion of the drum; and a mount bracket having a portion for attaching the backing plate and fixed to a vehicle body,
wherein the mount bracket is constructed by a structure substantially in a shape of a flat plate having a circular plate portion overlapping the circular disc portion of the backing plate and a flange portion extended from an outer periphery of the circular plate portion to constitute a portion for attaching the vehicle body, and
wherein the pair of brake shoes, the shoe drive mechanism and the anchor pin are directly attached to the circular plate portion of the mount bracket without interposing the backing plate.
Further, according to the above-described constitution, the mount bracket is constructed by the structure substantially in the shape of the flat plate which is a simple two-dimensional structure; therefore, the mount bracket can be formed by pressing similar to the backing plate or the like.
Further, there is constructed a constitution in which the pair of brake shoes, the shoe drive mechanism and the anchor pin are directly attached to the circular plate portion of the mount bracket without interposing the backing plate; therefore, when the backing plate is replaced in accordance with wear of a sliding portion (edge face) thereof, it is not necessary to remove or reattach the brake shoes, the shoe drive mechanism or the like. That is, only the backing plate may be removed by itself, and a part to be replaced may newly be attached thereto.
Further, according to the present invention, the drum brake may be characterized in that the mount bracket is formed by pressing a metal plate.
Further, by constructing the above-described constitution, in comparison with the conventional cast product or forged product, a considerable light-weighted structure can be realized.